1. Technical Field
The present invention generally relates to a process for the purification of water used in semiconductor manufacturing. More specifically, the present invention relates to a process that uses ultraviolet activated persulfate to decompose organic compounds in both pure and spent process water streams in semiconductor manufacturing facilities.
2. Background Art
Reducing TOC in water using ultraviolet light activated aqueous persulfate is known. It is an established method of decomposing organic compounds in water and is discussed in, for instance, U.S. Pat. No. 4,277,438, to Ejzak, which teaches a batch process of preparing water samples for the measurement of TOC by: (1) persulfate addition, (2) irradiation with an extreme dose of UV (which also heats the sample) to activate the persulfate to oxidize any TOC to carbon dioxide and water. U.S. Pat. No. 5,443,991, by Godec et al, teaches a similar method.
U.S. Pat. No. 5,571,419, to Obata et al, discloses a method of producing Ultra Pure Water (UPW) having a low concentration of organic matter. The purification method requires the following process for the water to be treated: (1) pH adjustment to less than 4.5, (2) addition of an oxidizing agent (such as a persulfate salt), (3) heating of the water to preferably a minimum of 110° C. and more preferably to 120° to 170° C., and (4) cooling the water to the temperature required for use.
The prior art also includes references showing an advanced oxidation process to destroy organic compounds in wastewater, including U.S. Pat. No. 5,762,808, to Peyton, and U.S. Pat. No. 6,096,283, to Cooper et al.
However, despite improvements in this technology, there remains a need for an improved method of producing a reliable, continuous source of low TOC UPW for the semiconductor industry and other industries that require ultrapure water with controlled total organic carbon. The novelty of the present invention is the UV activation of persulfate salt to produce high oxidation potential radicals at ambient temperature, in non-pH adjusted water to purify UPW prior to discharge from the Point of Distribution (POD), prior to the Point of Connection (POC) (typically labeled as the Point of Use or POU), and to purify spent UPW for reuse on a continuous basis.
The foregoing patents reflect the current state of the art of which the present inventors are aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicants' acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.